Antibiotic resistance of Pseudomonas aeruginosa from ocular samples in Canada: a 25-year analysis

To identify trends in antibiotic resistance patterns of Pseudomonas aeruginosa (PA) over a multi-decade period and analyse clinical outcomes.

PA isolates from ocular samples were collected over a 25-year time period in British Columbia, Canada. Source and antibiotic resistance were recorded. Demographic data, previous ocular history and clinical outcomes of patients with PA keratitis were analysed and compared in moxifloxacin-resistant versus moxifloxacin-sensitive PA keratitis cases.

321 ocular isolates of Pseudomonas were identified, 297 (92.5 %) of which were PA (101, 34 % cornea samples). Resistance to chloramphenicol was 88.7 %, 23.7 % to moxifloxacin and 10.1 % to meropenem. An increase in moxifloxacin resistance and non-susceptibility was noted, with a decrease in tobramycin resistance. The same trend was not observed for other fluroquinolone antibiotics. 14 (4.7 %) PA isolates were multi drug-resistant. 53 PA corneal isolates were included in the clinical analysis: 21 (40 %) sensitive, 17 (32 %) intermediate and 15 (28 %) resistant to moxifloxacin. Non-susceptible PA patients were older, more frequently non-contact lens wearers and a had a higher prevalence of previous ocular surgeries and topical treatment. A lower clinical response to initial treatment was observed in resistant cases. Need for surgery and complications were higher among moxifloxacin-resistant cases.

This study reports for the first time in North America a progressive and significant increase in moxifloxacin resistance among PA isolates. Overuse of topical moxifloxacin may be underlying this finding. Given the worse clinical outcomes in resistant cases, we would caution against the use of moxifloxacin alone as empirical treatment of infectious keratitis.